Failure Mode and Effects Analysis (FMEA) Additional material to execute FMEA exercise

Definitions Failure Mode: is the way in which the failure is manifested. Failure effect: is the consequence of the failure. Failure cause: is what induces the failure. Escalante (2003)

Failure Mode and Effects Analysis Abbreviated Approach O c u r S C D Actions Results e l Potential Causes/ Mechanisms(s) Failure Current e R Item Potential Potential v a t P Responsibility s Controls e N Failure Effect(s) of Recommended & Target s Actions S e v O c D e t R P N Function Mode Failure c Action(s) Completion Date Prevention/Detection Taken What can be done? What How bad is it? - Design changes are the Effect(s)? What did they do and what are the outcomes - Process changes How often does it happen? What are the functions, features or requirements? - Special controls - Changes to standards, procedures, or guides What can go wrong? What are the Cause(s)? - No Function How good is this method at detecting it? - Partial/ Over/ Developed by: Edgardo J. Escalante, Auburn University-ITESM What are the functions? - Land landing of the CEV What can go wrong? - Airbags partially deploy What are the effects? - Impact loads significant How bad is it? - Structural damage to the CEV Degraded Function Who is going to do it and when? - Intermittent How can this Function be prevented and detected? - Unintended Function

(9) Name of the item and its intended function (purpose/objective). FMEA (cont.) Item/Function Potential Potential S C Potential Cause(s)/ Failure Effect(s) e l Mechanism(s) of Mode of failure v a failure s (9) (10) (11) (14) (12) (13) (9) Name of the item and its intended function (purpose/objective). (10) Include specific problems, failures, defects (anti-functions) of the analyzed system(*) and its functions. Use physical terms. (11) The effect of failures in the function of the analyzed system, as they would be perceived by the customer (internal/external). (12) Evaluation of the severity of the effect of the failure to the next system or to the internal/external customer. Sometimes large values of severity can be reduced by means of design reviews that compensate or mitigate the resulting severity. (*) subsystem or component

FMEA SEVERITY EVALUATION CRITERIA EFFECT CRITERIA: Severity of Effect RANK Hazardous- without warning Very high severity ranking when a potential failure mode affects safe vehicle operation and/or involves noncompliance with government regulation without warning 10 Hazardous- with warning Very high severity ranking when a potential failure mode affects safe vehicle operation and/or involves noncompliance with government regulation with warning 9 Very High Vehicle/item inoperable (loss of primary function). 8 Vehicle/item operable but at a reduced level of performance. Customer very dissatisfied. High 7 Vehicle/item operable but Comfort/Convenience item(s) inoperable. Customer dissatisfied. Moderate 6 Vehicle/item operable but Comfort/Convenience item(s) operable at a reduced level of performance. Customer somewhat dissatisfied. Low 5 Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by most customers (greater than 75%). Very Low 4 Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by 50% of customers. (D,F,GM. FMEA, 2001) Minor 3 Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by discriminating customers (less than 25%). Very Minor 2 None No discernible effect. 1

(D,F,GM. FMEA, 2001) Effect PROCESS   Effect   PROCESS ------------------------------------------------------ Criteria: SEVERITY of Effect   Ranking   Hazardous- without warning  Very high severity ranking when a potential failure mode affects safe operation and/or involves noncompliance with regulations without warning. Or may endanger operator without warning.   10   Hazardous- with warning  Very high severity ranking when a potential failure mode affects safe operation and/or involves noncompliance with regulations with warning. Or may endanger operator with warning.   9 In the third edition this table is presented in two columns but the information is the same (customer effect and manufacturing/assembly effect).   Very high  Product/item inoperable, with loss of primary function. Or 100% of product may have to be scrapped or repair time >1h.   8   High  Product/item operable, but at reduced level of performance. Customer dissatisfied. Or product may have to be sorted and less than 100% scrapped. Repair time between 0.5 and 1h.   7 (D,F,GM. FMEA, 2001)   Moderate Product/item operable, but comfort/convenience inoperable. Customer dissatisfied. Or a portion (less than 100%) of the product may have to be scrapped with no sorting. Repair time less than 0.5h   6

  Low Product/item operable, but comfort/convenience operable at a reduced level. Or than 100% of the product may have to be reworked with no sorting. Repairing off-line. 5 Very Low Fit and finish/squeak and rattle item does not conform. Defect noticed by most customers (greater than 75%). Or product may have to be sorted with no scrap, and a portion (less than 100% reworked. 4 Minor Fit and finish/squeak and rattle item does not conform. Defect noticed by 50% of the customers. Or a portion (less than 100%) of the product may have to be reworked with no scrap. On-line but out-of-station. 3 Very Minor Fit and finish/squeak and rattle item does not conform. Defect noticed by discriminating customers (less than 25%). Or a portion (less than 100%) of the product may have to be reworked with no scrap. On-line but in-station. 2 None No discernible effect. Or slight inconvenience to operation or operator, or no effect. 1 (D,F,GM. FMEA, 2001)

(13) Indicates any special characteristic (critical, key, major) FMEA (cont.) Item/Function Potential Potential S C Potential Cause(s)/ Failure Effect(s) e l Mechanism(s) of Mode of failure v a failure s (9) (10) (11) (14) (12) (13) (13) Indicates any special characteristic (critical, key, major) that will require special controls. Some of the D, F, GM special symbols can be used. (An indication of criticality is when severity is 9 or 10, being the occurrence and detection geater than 3. (Stamatis, 1995)). (14) Describe what causes the failure modes. Discover the root causes.

Summary of FMEA S C Potential causes/ mechanism of failures Product/ function Potential failure mode Potential failure effects e l v a s Name of the item and its intended function (purpose/objective). Include specific problems, failures, defects (anti- functions) of the analyzed system(*) and its functions. Use physical terms The effect of failures in the function of the analyzed system, as they would be perceived by the customer (internal/external) Describe what causes the failure modes. Find the root cause. Typical causes: Use field data, previous FMEAs, warranties, etc. Incorrect material spe- cified, Inadequate design life assumption, Over-stressing Insufficient lubrication capability Begin with previous FMEAs, brainstorming. Use technical terms. Examples: Cracked, loosened, fractured, leaking... Examples: Noise, erratic operation, unstable, inoperative... Typical mechanisms: Wear, fatigue, corrosion Summary of FMEA

FMEA (cont) (15) (16) (17) (18) (19) (20) (15) Frecuency of the cause from 1 to 10. Statistically assigned if having information about similar components, systems or sub-systems. Otherwise use the following table. (16) List the verification/validation design activities or others related activities. The prevention controls are preferred. It’s recommended to use two columns to define the two types of controls: (P) for prevention, (D) for detection.

DESIGN OCCURRENCE EVALUATION Probability of Likely Failure Rates Over Design Ranking Failure Life Very High: ³ 100 per thousand vehicles/items 10 Persistent failures 50 per thousand vehicles/items 9 High: 20 per thousand vehicles/items 8 Frequent failures 10 per thousand veh icles/items 7 DESIGN OCCURRENCE EVALUATION Moderate: 5 per thousand vehicles/items 6 Occasional failures 2 per thousand vehicles/items 5 1 per thousand vehicles/items 4 Low: Relatively 0.5 per thousand vehicles/items 3 (D,F,GM. FMEA, 2001) few failures 0.1 per thousand vehicles/items 2 Remote : £ 0.01 per thousand vehicles/items 1 Failure is unlikely

FMEA (cont) There are 2 type of controls according to its importance: (15) (16) (17) (18) (19) (20) There are 2 type of controls according to its importance: i) Prevention. To prevent the cause/mechanism or the effect/failure mode, or reduce its occurrence. ii) Detection. To detect the cause/mechanism or the effect/failure mode by either analytic of physical methods. Preventive controls are related to the reduction of OCCURRENCE and not to the evaluation of DETECTION

DFMEA (cont) (15) (16) (17) (18) (19) (20) (17) Is the evaluation associated to the best detection control listed in the design control (relative evaluation for every individual FMEA). A scale from 1 to 10 is used. The suggested evaluation criteria is shown in the following table. (18) (Risk Priority Number). Evaluation of the design’s risk. Varies between 1 and 1000: RPN= (S)x(O)x(D)

(D,F,GM. FMEA, 2001)

FMEA (cont) (15) (16) (17) (18) (19) (20) (19) Attention should be focused on high values of severity, and high RPN, and in general, independently of the RPN when the severity is 9 or 10. The goal is first to reduce severity, then reduce ocurrence, and last to reduce detection. It is desirable that the recommended actions reduce the risk and increase customer satisfaction by means of an improved design.

FMEA (cont) -Only the design reviews can reduce severity. (15) (16) (17) (18) (19) (20) -Only the design reviews can reduce severity. -To reduce occurrence the causes or failure mechanisms must be eliminated or controlled through design reviews. -To improve detection, the design verification and validations actions should be increased. If there are no actions, write “none”. (20) Define the responsible person and the completion date.

(prevention/detection) Current design controls (prevention/detection) R P N Responsibility & target completion date c e Recommended actions u t r e r c List the design verification and validation activities. Include current control like field tests, laboratory studies and prototype testing applied to this or to similar designs. There are 2 type of controls according to its importance: i) Prevention. To prevent the cause/mechanism or the effect/ failure mode, or reduce its occurrence. ii) Detection. To detect the failure mode by either analytic of physical methods. Determine and apply improvement actions. If they are not necessary write the word “none” To reduce occurrence the causes or failure mechanisms must be eliminated or controlled through design reviews. To improve detection, the design verification and validations actions should be increased. If there are no actions, write “none”. It’s preferable to reduce -in that order, severity, occurrence and detection Define the responsible person and the completion date Summary of FMEA (cont.)

FMEA (21) (22) (21) Register the implementation date and a brief description of the action taken. (22) After the implementation of the corrective actions, re-evaluate the severity, occurrence and detection. If necessary repeat steps 19-22. Don´t forget the follow up actions.

Register the implementation date and a ACTION RESULTS S O D R e c e P Actions taken v u t N r c Register the implementation date and a brief description of the action taken. Re-evaluate RPN.